As shown in FIG. 1, a memory cell 100 of magnetic random access memory (MRAM) has a structure where a magnetoresistive element 101 and a select transistor 102 are electrically connected in series. The source electrode, drain electrode, and gate electrode of the select transistor 102 are electrically connected with a source line 103, with a bit line 104 via the magnetoresistive element 101, and with a word line 105, respectively. The basic structure of the magnetoresistive element 101 is a three-layer structure in which a non-magnetic layer 108 is sandwiched by two ferromagnetic layers, namely a first ferromagnetic layer 106 and a second ferromagnetic layer 107. In the illustrated example, the first ferromagnetic layer 106 has a fixed magnetization direction and serves as a reference layer. The second ferromagnetic layer 107 has a variable magnetization direction and serves as a recording layer. This magnetoresistive element 101 has a low resistance when the magnetization direction of the first ferromagnetic layer 106 and the magnetization direction of the second ferromagnetic layer 107 are mutually parallel (P state), and a high resistance when they are anti-parallel (AP state). With MRAM, this change in resistance is made to correspond to bit information of “0” and “1”. Bit information is written through spin-transfer torque magnetization switching caused by the current flowing through the magnetoresistive element 101. When a current flows from the reference layer to the recording layer, the magnetization of the recording layer becomes anti-parallel to the magnetization of the reference layer, and the bit information becomes “1”. When a current flows from the recording layer to the reference layer, the magnetization of the recording layer becomes parallel to the magnetization of the reference layer, and the bit information becomes “0”. Since the speed of magnetization switching by current is approximately 1 nanosecond, MRAM can be written to at an extremely high speed. In addition, since bit information is recorded by way of the magnetization direction of the recording layer, MRAM is non-volatile, and is able to keep standby power consumption low. Accordingly, there are high expectations for MRAM as a next-generation memory.
In addition, although the case illustrated in FIG. 1 is one where the first ferromagnetic layer 106 of the magnetoresistive element 101 is a reference layer, and the second ferromagnetic layer 107 a recording layer, it would still similarly operate as MRAM even if the first ferromagnetic layer 106 of the magnetoresistive element 101 were made to be a recording layer with a variable magnetization direction, and the second ferromagnetic layer 107 a reference layer with a fixed magnetization direction. In this case, too, when a current flows from the reference layer to the recording layer, the magnetization of the recording layer becomes anti-parallel to the magnetization of the reference layer, and the bit information becomes “1”. When a current flows from the recording layer to the reference layer, the magnetization of the recording layer becomes parallel to the magnetization of the reference layer, and the bit information becomes “0”.